Metallized films have been used as a packaging material, for example, in the form of a layered polypropylene film/aluminum foil structure. However, many such conventional films have a weak adhesive force between the base film and the metallic layer as well as poor printability and adhesive properties. Japanese Patent Application No. 55-52333/1980 discloses that a cause of these difficulties is the migration or transfer of additives in the base polypropylene film, such as acid neutralizers, slip agents, antioxidants or other additives, to the metallized surface to deteriorate the properties of the metallized film.
U.S. Pat. Nos. 4,508,786 and 4,487,871 to Ishibashi et al. disclose that low molecular weight antioxidants and fatty acid derivatives such as higher fatty acid salts, fatty amides, fatty esters and fatty amine derivatives have a particularly negative effect on the film characteristics. The Ishibashi et al. patents further disclose a polyolefin resin of blended propylene-.alpha.-olefin crystalline copolymer and high density polyethylene (HDPE) containing a phenolic antioxidant and/or phosphonite antioxidant additive and an inorganic filler for making metallized films.
However, there is a need in the art for more economical resins for producing metallized films having good adhesion and heat sealability and which provide a long shelf life.